The manufacture of such reinforcements is effected conventionally by forming angled plies, in which the reinforcement cords form a specified angle with the longitudinal direction of the ply, and which are prepared flat in the form of semi-finished products which are laid by winding over a reference form during assembly of the tire. The reference form is generally mounted on a frame having means for setting the same in rotation.
Another manner of proceeding includes laying cords or lengths of cords directly in their final place on the laying form or tire blank. Apparatus permitting this type of manufacture is described by way of non-limiting example in the publications EP 0 519 295, EP 580 055, EP 1 231 049, or even EP 1 426 170, which describe laying apparatuses wherein the reinforcement cord is laid by a cord guide carried by a rotary or oscillating laying arm and is then stuck into position on the laying form by applicators, or in the publications EP 0 248 301, EP 0 845 348 or EP 0 845 349 which describe laying apparatuses wherein the reinforcement cords are projected individually on to the element defining the reinforcement geometry. A cord guide can make it possible to adjust the final trajectory of the length of cord so as to improve reproducibility and precision of laying.
The invention relates in particular to laying apparatuses such as those described above.
These apparatuses comprise means of calling for cord from a source such as a spool, and have in common that the cord or lengths of cords are set in motion in space in a laying plane whose intersection with the laying form or tire blank forms a line, part of which coincides with the cord or the length once laid.
The term cord must be understood in an entirely general manner and comprises cords in the form of monofilaments, multifilaments, a cable, a plied yarn or equivalent assembly, whatever the material forming the cord or the surface treatment used to enhance its bonding with the rubber or to allow its adhesion direct to the support during projection.
So as to realise positioning of the cords or lengths of cords, in conformity with the structure of the tire, it is advantageous to lay them on the tire blank according to one position (generally centred relative to the equator of the torus formed by the tire blank), and at a specified angle relative to the longitudinal direction.
The direction of the cord, once laid, makes a specified angle α with the circumferential direction of the tire. This angle α may vary from 0 to 90°. However, in the particular case of crown reinforcements, the angle α is between 15° and 40°. Furthermore, the device for laying lengths of cord of the type described above must be aligned on the one hand with the centre of the tire blank placed on the reference form, and on the other hand oriented precisely relative to the circumferential direction so as to lay the cords or lengths of cords at the desired angle α and in the prescribed position.
To this end, the apparatus for laying lengths of cord is mounted on a frame via an articulated system which is capable, for the purposes of adjustment, to make the apparatus for laying the cords or lengths of cords rotate by a specified angle α about a virtual axis ZZ′. The frame supporting the laying device is aligned geometrically with the frame supporting the reference form.
The axis ZZ′, about which the laying apparatus revolves, is generally contained in the equatorial plane of the tire blank or of the form acting as a reference for the same, and intersects perpendicularly with the virtual axis of rotation XX′ of the reference form at a specified point. The equatorial plane E is defined as being the plane passing through the axial centre of the blank or of the form acting as a reference and being perpendicular to the axis of rotation XX′ of the blank or reference form. In general, when a radial section of a tire blank or form is observed, the point most remote from the axis of rotation and located on the surface of the tire blank or form XX′ belongs to the equatorial plane.
Although this mode of setting up the device for laying cords is satisfactory by virtue of its low bulk and excellent ease of integration with the other laying devices, it is nevertheless difficult to adjust and keep in a specified position with the required degree of precision for laying of the cord or lengths of cords.
It is found in fact that the presence of articulations and arms which are necessary for controlling the rotary movement of the laying apparatus about the axis ZZ′ brings about an accumulation of mechanical play which leads to some imprecision in the positioning of the cord in space, which may in turn lead to a variation in the angular position of the cords or lengths of cords of the order of some degrees. This imprecision is incompatible with the industrial standard of precision and reliability sought for the manufacture of high-performance tires. This imprecision may also be aggravated by the heavy mechanical stress generated by the rapid rotation of the elements of the apparatus for laying cords or lengths of cord, which is transmitted to the frame supporting the laying apparatus via control arms and articulations.